The 200-300 Hz area sounds too loud in my listening room. I would like to do
something about this by adjusting my speakers response curves, becouse they are
certainly a part of the problem. One option would be to modify the speakers
crossover, but how would a Helmholz resonator inside the speaker enclosure work
for this purpose?

I would also appreciate if someone could point me to some general guidelines
for how a Helmholz resonator should be designed.

"tee@m..." wrote:
>
> Hello all.
>
> The 200-300 Hz area sounds too loud in my listening room. I would like to do
something about this by adjusting my speakers response curves, becouse they are
certainly a part of the problem. One option would be to modify the speakers
crossover, but how would a Helmholz resonator inside the speaker enclosure work
for this purpose?

If the problem is the speaker response curve, I'd certainly suggest
adjusting the crossover or applying electronic equalization before I'd
add treatment to the room (or speaker). Adjusting the speaker's
response is a "minimum phase" situtation - a correction to the frequency
response maintains the correct phase relationships. This is different
from problems introduced by the room due to modes or reflections, where
adjusting the frequency response of the source will not address phase
issues - so you wind up moving the problem around instead of actually
addressing it. As a simple example of this, consider a room that is
"boomy" at a certain frequency at a given location. Cutting that
frequency with an EQ at the source may reduce the problem at that spot,
but it will make that frequency weak everywhere else. This is because
the problem isn't that the source is producing too much signal at the
offending frequency, but because the modes of the room are combining to
trap energy at that frequency - there is a time/phase issue involved
(due to the speed of sound/wavelength/room dimension combination) that
can't be addressed by adjusting the frequency response. On the other
hand, if the speaker does have a "bump" in its response, EQing it out
will flatten the response at that frequency (relative to the un-EQed
response) everywhere in the room.

I'd be worried about ringing from the resonator, as well as phase
issues. If the problem really is speaker response, EQ - either from the
crossover or an additional unit, not treatment is the ticket. But I
have my doubts that this is really the case - the frequencies you are
having trouble with are typical for modal problems. If the problem
changes in intensity or frequency as you move your ears or speakers
around the room, it's definitely modal. In this case, apply treatment
to the room, not the speakers.

>
> I would also appreciate if someone could point me to some general guidelines
for how a Helmholz resonator should be designed.
>

If you are hellbent on building Helmholz resonators, Everest's Master
Handbook of Acoustics discusses several different designs and includes
the math you need to calculate the resonant frequencies. Keep in mind
that designing High-Q Helmholz resonators is as much art as science -
they are difficult to get exactly on a target design frequency.

<< > The 200-300 Hz area sounds too loud in my listening room. I would like
to do something about this by adjusting my speakers response curves, becouse
they are certainly a part of the problem. One option would be to modify the
speakers crossover, but how would a Helmholz resonator inside the speaker
enclosure work for this purpose?
>>

This would change the designed internal volume of the speaker.
It sounds to me like you would be much better off designing a
Helm. Res. the take care of the room mode problem. If the problem
IS actually the speaker response, get better speakers. You can't do
a mix on speakers that aren't relatively flat.

> Hello all.
>
> The 200-300 Hz area sounds too loud in my listening room. I would like to
> do something about this by adjusting my speakers response curves, becouse
> they are certainly a part of the problem. One option would be to modify the
> speakers crossover, but how would a Helmholz resonator inside the speaker
> enclosure work for this purpose?
>
> I would also appreciate if someone could point me to some general
> guidelines for how a Helmholz resonator should be designed.
>
> -T.
>

Yikes .. why not just disconnect the wires from the back of those speakers?

Please note that implementing EQ will also affect the phase relationship of
the signals that are processed through that EQ. In fact, I've read that it
is this phase shift that is often responsible for producing most of the
"character" or "signature" sound of a particular EQ device. "Pure"
theoretical EQ (amplitude change without phase shift) is not possible with
an "Infinite Impulse Response" filter (IIR), which all hardware EQ's are.
It is only possible with a "Finite Impulse Response" (FIR) filter, which can
be implemented with a software algorithm (like in a DSP chip).

I once read an article on this topic in MIX Magazine by Stephen St. Croix.
He described a test that was performed to compare how people reacted to the
sound of an IIR filter versus a FIR filter EQ. The interesting result was
that people tended to boost/cut the FIR EQ by a greater amount than the IIR
EQ, in order to achieve a similar subjectively satisfying result. The
reason was that the phase shift caused the IIR EQ effect to be much more
noticeable than the pure amplitude boost/cut of the FIR EQ. The people did
not realize that it was the phase shift they were hearing. Most of us have
never heard theoretically perfect EQ to use a reference; all our life what
we have come to know as EQ has always included a phase shift.

I have been trying to find out if some of these software plug-ins for Pro
Tools use FIR filters, but every time I ask the Pro Tools rep at product
demo event they just look at me funny and have no idea what I'm talking
about. If anyone out there can tell me if there are any EQ products out
there using FIR filters, please let me know. Thanks.

"tee@m..." wrote:
>
> Hello all.
>
> The 200-300 Hz area sounds too loud in my listening room. I would like to
do something about this by adjusting my speakers response curves, becouse
they are certainly a part of the problem. One option would be to modify the
speakers crossover, but how would a Helmholz resonator inside the speaker
enclosure work for this purpose?

If the problem is the speaker response curve, I'd certainly suggest
adjusting the crossover or applying electronic equalization before I'd
add treatment to the room (or speaker). Adjusting the speaker's
response is a "minimum phase" situtation - a correction to the frequency
response maintains the correct phase relationships. This is different
from problems introduced by the room due to modes or reflections, where
adjusting the frequency response of the source will not address phase
issues - so you wind up moving the problem around instead of actually
addressing it. As a simple example of this, consider a room that is
"boomy" at a certain frequency at a given location. Cutting that
frequency with an EQ at the source may reduce the problem at that spot,
but it will make that frequency weak everywhere else. This is because
the problem isn't that the source is producing too much signal at the
offending frequency, but because the modes of the room are combining to
trap energy at that frequency - there is a time/phase issue involved
(due to the speed of sound/wavelength/room dimension combination) that
can't be addressed by adjusting the frequency response. On the other
hand, if the speaker does have a "bump" in its response, EQing it out
will flatten the response at that frequency (relative to the un-EQed
response) everywhere in the room.

I'd be worried about ringing from the resonator, as well as phase
issues. If the problem really is speaker response, EQ - either from the
crossover or an additional unit, not treatment is the ticket. But I
have my doubts that this is really the case - the frequencies you are
having trouble with are typical for modal problems. If the problem
changes in intensity or frequency as you move your ears or speakers
around the room, it's definitely modal. In this case, apply treatment
to the room, not the speakers.

>
> I would also appreciate if someone could point me to some general
guidelines for how a Helmholz resonator should be designed.
>

If you are hellbent on building Helmholz resonators, Everest's Master
Handbook of Acoustics discusses several different designs and includes
the math you need to calculate the resonant frequencies. Keep in mind
that designing High-Q Helmholz resonators is as much art as science -
they are difficult to get exactly on a target design frequency.

"Hill, Scott (S.E.)" wrote:
>
> Please note that implementing EQ will also affect the phase relationship of
> the signals that are processed through that EQ. In fact, I've read that it
> is this phase shift that is often responsible for producing most of the
> "character" or "signature" sound of a particular EQ device. "Pure"
> theoretical EQ (amplitude change without phase shift) is not possible with
> an "Infinite Impulse Response" filter (IIR), which all hardware EQ's are.
> It is only possible with a "Finite Impulse Response" (FIR) filter, which can
> be implemented with a software algorithm (like in a DSP chip).
>

This is true, but since a cross-over is present there is already impact
on the phase relationship of the signal from the amp vs that reaching
the speakers.

This is also not the same thing as trying to correct for "non-minimum
phase" issues introduced by the room by EQing the source - I'm not
suggesting that EQing doesn't introduce phase shifts, but that adjusting
the frequency response with an EQ will not account for the phase
response of the room. Bottom line - EQing your speakers to correct
their response may or may not degrade the sound in the room, depending
on the signal and the listener's sensitivity to phase issues on that
particular signal, but it won't fix problems due to modes or reflections
(comb filtering) in the room, it will merely move them around.

Adding a Helmholz resonator to the speaker itself (as per the original
question) will almost definitely have impacts on the speaker's
performance beyond attenuating the resonator's design frequency and they
will be much more apparent than equal attenuation at the same frequency
achieved by EQ (unless it's a really nasty EQ).

The advent of affordable spectrum analysis in the 70's lead many people
to try to "EQ away" problems in Control Rooms (and other critical
listening rooms). When these problems were not in the signal path or
speaker, but in the room, the solution was often worse than the original
situation. In the best case, the solution resulted in a very tiny sweet
spot where things were balanced and generally crappy sound (by
comparison) everywhere else. This lead to a backlash and today many
people won't use EQs in the monitor chain at all, but they do have their
place for adjusting for inadequacies in the signal chain and monitor
response (especially if you have an EQ and can't afford better monitors,
amp and/or cross-overs). As with all tools, the trick is knowing when
to use it and when to use something else.

In the end, it's almost always better to adjust for problems using room
treatments, speaker, mic and listener placement or different speakers,
mics or instruments rather than EQing.

> I have been trying to find out if some of these software plug-ins for Pro
> Tools use FIR filters, but every time I ask the Pro Tools rep at product
> demo event they just look at me funny and have no idea what I'm talking
> about. If anyone out there can tell me if there are any EQ products out
> there using FIR filters, please let me know. Thanks.
>
> S. Hill
>

--- In acoustics@y..., "John C. Griggs" <johng@c...> wrote:
> "tee@m..." wrote:
> >
> > Hello all.
> >
> > The 200-300 Hz area sounds too loud in my listening room. I would
like to do something about this by adjusting my speakers response
curves, becouse they are certainly a part of the problem. One option
would be to modify the speakers crossover, but how would a Helmholz
resonator inside the speaker enclosure work for this purpose?

Wow John - that would be doing a very brave thing. I would suggest
the first thing to do would be to identify the source of the problem.
How do mixes translate from your room to another? Is it the
speakers? Is it the room itself? Identify the problem and do
something about that. If it is the speakers - what is wrong with them
and address it. If it is the room, address that.

I would also appreciate if someone could point me to some general
guidelines for how a Helmholz resonator should be designed.

Have a look at my friend John Sayers website, one of the best studio
design sites on the web: http://www.lis.net.au/~johnsay/ ... and if
you look under "studios under construction" you can see some pics of
my place as well.